With the worldwide rapid economic growth, losses caused by friction and abrasion in various industries increases accordingly, and the energy crisis gets increasingly severe. According to foreign statistics, 30% of the primary energy around the world is consumed by friction, and about 80% of machine parts get failed due to abrasion. It is roughly estimated that the economic losses caused by friction and abrasion in China exceed a trillion CNY annually. Therefore, the development of a novel anti-friction and lubrication technique becomes a significant research area in energy and resources saving. In recent years, the discovery of superlubricity phenomenon provides a new and important method to solve the problem of energy wastage. It is generally known that a superlubricity state refers to a lubricating state when a magnitude of the coefficient of the sliding friction is equal to or less than 0.001 (referred to as an ultra-low friction coefficient). In the superlubricity state, the friction coefficient is greatly reduced by orders of magnitude, compared to traditional oil lubrication. The superlubricity state has an extra-low abrasion rate which is almost close to zero. The realization and wide application of the superlubricity state greatly reduces the wastage of energy and resource, and significantly improves the service quality of major motion components.
In fact, since numerous factors would affect the superlubricity state and these factors are mutually coupled, the further research on the superlubricity theory and technology is greatly restricted. Nanoscale single-point contact (i.e. the size of the contact area is nanoscale) can eliminate various disturbing factors from the outside like multi-point contact at the macro level etc., and facilitate the quantitative analysis of the superlubricity process. However, the measurement of the ultra-low friction coefficient under the nanoscale single-point contact state is an acknowledged technical problem, which is difficult mainly in the following two aspects. First, the nanoscale single-point contact is usually realized by an atomic force microscope, while the atomic force microscope is mainly applied to surface shape scanning, mechanical property testing, etc. The use of the atomic force microscope almost does not focus on the ultra-low friction coefficient measurement. Second, in most conditions, the resolution of the friction coefficient reported in the literatures is in the magnitude of 0.01, which is far from achieving the measurement of friction coefficient with the resolution in the magnitude that is equal to or less than 10−6 (i.e. the higher resolution <10−6). When the friction coefficient is further reduced to the magnitude that is equal to or less than 10−6, the signal of the friction force is completely covered by the system noise, so the signal of the friction force is unmeasurable.
To this end, it is significant to optimize and improve the existing measurement technique of friction coefficient of nanoscale single-point contact to realize the measurement of ultra-low friction coefficient with the resolution in the magnitude that is equal to or less than 10−6.